U.S. Pat. No. 4,540,495 (Holloway, 1985, the disclosure of which is incorporated herein by reference) is concerned with a process for the treatment of municipal solid waste (MSW). It discloses that the waste comprises inorganic, organic and synthetic fractions. The major portion of the inorganic fraction is said to be metal and glass containers, ceramics, masonry, building materials and the like. The organic fraction which is stated to comprise 80 wt % of MSW consists of lignocellulose e.g. paper products together with yard (garden) waste and food waste. The synthetic fraction comprises plastics containers, plastics film and other synthetic plastics products. The organic fraction is said to represent the industrial world's largest economically accessible source of lignocellulose feedstock for conversion into alcohol and other industrial chemicals. It is further explained that MSW is an environmental concern owing to the dwindling availability of landfill sites. A treatment process is disclosed in which MSW is fed into a pressure vessel, subjected to heat at 132-160° C. (270-320° F.) under a pressure of from 276-517 kPa (40 to 75 psi) for 30-90 minutes with introduction of steam to give a residual moisture content of 60-70%, discharged and classified to give an organic fraction as fines with moisture content 60-70%.
U.S. Pat. No. 4,884,351 (Holloway) discloses an autoclave for the handling of municipal solid waste which is in the form of a cylindrical vessel inclined at about 15° to the horizontal and having frustoconical ends each closed by a hinged hatch. The hatch at the higher end serves as inlet for the waste to be processed and that at the lower end serves as an outlet for processed waste. The autoclave is supported for rotation about its longitudinal axis and has internal flighting angled at about 30° to its axis by which in a forward rotation mode the fighting directs material to the lower end of the autoclave during filling and/or discharge and in a reverse rotation mode material being processed is conveyed upwardly and axially towards the higher end and is mixed and agitated, reverse rotation being during processing of the material. Heating is by introduction of saturated steam via an inlet on the axis of the vessel and at the upper end thereof, the processing temperature being 48-108° C. (120-228° F.) preferably 88-102° C. (190-215° F.) to rupture bags of plastics film but to leave low density plastics materials substantially intact so that they are easily identifiable and separable from other components of the waste.
U.S. Pat. No. 4,974,781 (Placzek) is similar and has as its object the re-pulping of re-pulpable waste material, the water content of the waste typically being 50 wt %. Waste and water is added to a rotary autoclave or so-called “trommel” to give a moisture content of at least 30% of the moisture absorptive components of the waste, 65-75% moisture content being considered an optimum. A working temperature of 100-115° C. (212-240° F.) is considered best for plastics recovery and 115-149° C. is considered best for re-pulping. The autoclave which in use is downwardly inclined at an angle of 4° is provided with lifting blades and directional flighting, a waste inlet at its upper end and a waste outlet at its lower end. The inlet and outlet each have a closure device in the form of a sliding gate valve which is movable axially towards or away from the inlet or the outlet. Steam and water can pass into the autoclave from its lower end via injection piping that extends into and rotates with the autoclave, the piping being connected to a rotary seal on the axis of rotation of the autoclave adjacent the discharge end
U.S. Pat. No. 5,445,329 (Anderson) discloses a rotary autoclave mounted to a support frame by trunnions so that the axis of the autoclave can be tilted in either direction so that in one end of its tilting travel its forward end faces downwardly at 45° to the vertical and at the other end of its tilting travel the forward end faces upwardly at 22° to the vertical, these corresponding to loading and discharge states respectively. The vessel is supported in the frame on rotary supports provided with strain gauge based load sensors and by thrust bearings. One end of the autoclave has a door for rotation and discharge of the load, and the other end of the autoclave is provided with an external manifold from which steam can be introduced into the autoclave as it rotates by means of a hollow shaft extending cantilever-wise into the interior of the vessel for a portion of its longitudinal extent, typically 15-25% of the total length of the vessel, the shaft being provided along its length with spaced apart openings or jets through which steam can be introduced into the interior of the autoclave. The strain gauged load sensors are in the form of rollers adjacent opposed ends of the autoclave and are provided for measuring the live load distribution within the vessel. Input from the sensors is used to effect an approximately equal distribution of the material located in the vessel during the treatment operation and to control the angle of inclination of the vessel so that if a sensor associated with a front vessel support detects a load significantly greater than a sensor associated with a rear vessel support, the front end of the vessel is raised so as to cause the material within the vessel to move towards the rear end thereof, this forming part of a so-called “automatic balancing” operation. Nothing is disclosed concerning the use of load sensors in an autoclave having a fixed axis of rotation.
U.S. Pat. No. 5,655,718 (Anderson, divided from U.S. Pat. No. 5,445,329) relates to a method of treating process material, comprising: introducing a first batch of process material to be treated into an interior of a first vessel which has a longitudinal axis; rotating the first vessel about its longitudinal axis; raising the temperature within the interior of the first vessel through the introduction of steam into the interior of the first vessel; introducing a second batch of process material to be treated into an interior of a second vessel; reducing the temperature in the interior of the first vessel while also increasing the temperature in the interior of the second vessel by venting steam from the interior of the first vessel and introducing the vented steam into the interior of the second vessel; continuing rotation of the first vessel after steam in the interior of the first vessel has been vented into the second vessel to facilitate drying of the process material in the first vessel; rotating the second vessel about its longitudinal axis while the first vessel is rotating; and emptying the first batch of process material from the first vessel.
Provision of axial steam inlets at both ends of the vessel is disclosed in U.S. Pat. No. 7,347,391 (Michalek), the vessel being supported so that its direction of tilt can be reversed in order to overcome the problem of load compaction.
Sterilizing waste by heat and pressure, separation of organic matter and fermentation followed by distillation to remove alcohol, centrifugation to remove fats and animal feed components and anaerobic digestion of the effluent to recover methane is disclosed in WO 82/01483 (Holloway), see also WO 2004/041733 (Anderson, Comprehensive Resources).
EP-A-2105414 (Anderson, Sterecycle, divided from a European application corresponding to WO 2004/041733) claims a method of treating waste material, including organic and inorganic materials with the organic materials including starches, cellulose and other carbohydrates, the method comprising: (a) subjecting the waste material to increased temperature, pressure and moisture within an apparatus by introducing steam into the apparatus; (b) increasing the temperature and pressure within the apparatus by an effective amount to cause the steam to reach a saturated state within the apparatus; (c) rapidly reducing the pressure within the apparatus to cause the steam to become superheated; (d) removing the material from the apparatus and passing the material through a screen to separate the material by size (e.g. passing material of size <12 mm); and (e) diluting the biomass obtained from the steam autoclaves with water and subjecting at least a portion of the diluted mixture to anaerobic digestion wherein the portion of the mixture is converted to one or more of a biogas suitable for use as fuel, and a residual sludge. In particular the process involves diluting at least a first portion of the material with water while agitating the resulting diluted mixture a sufficient amount and at an effective temperature to cause cellulose fibres that became twisted and tangled during processing within the apparatus to relax and straighten out or untangle. The specification explains that temperatures of between 126 and 132° C. (260-270° F.) reached within steam autoclaves have been found to enhance the characteristics of cellulose fibres separated from the biomass produced by the autoclaves. They further explain that paper fibre generally includes lignin that binds to the cellulose fibre, hemicellulose, which is the soluble portion of the cellulose, and cellulose, which is very difficult to solubilise unless it is treated with acids, etc. Because the softening point of the lignin is approximately 128° C. (262° F.), the temperatures reached within the steam autoclave causes the lignin that binds to the cellulose fibres to be softened, but the lignin is not heated enough to be crystallized. Low melting point plastics within the biomass form into small beads that are easily separated during subsequent density and size separations so as to not be included with the cellulose fibres used by the paper industry. Anaerobic digestion of the cellulosic material and hydrolysis of the cellulose during the autoclaving step in order to facilitate or improve the anaerobic digestion step is neither disclosed nor suggested.
WO 2009/095693 (Reclaim Resources) discloses a process and apparatus for recycling municipal solid waste comprising subjecting the waste to steam at 150-200° C. After steam treatment, the resultant material is separated into constituent parts and biomass and/or plastics subjected to further treatment which preferably produces bioethanol from the biomass and diesel from the plastics. As an alternative, some or all of the biomass may be gasified in order to produce hydrogen which may in turn be fed to a fuel cell to produce an electrical output. The biodiesel or bioalcohol can also be used to produce electricity. Conducting the autoclave steam treatment under a combination of thermal contact, temperature and pressure conditions such that the cellulosic component becomes significantly hydrolysed within the autoclave is neither disclosed nor suggested.
A further aspect of industrial autoclave design relates to a swing-aside locking door which is acknowledged in Wikipedia to be the most costly and important single piece of hardware in an autoclave. For autoclaves of diameter>four feet (1.2 meters) it is conventional to use a rotating locking ring arrangement or so-called “breech-lock door”. U.S. Pat. No. 2,841,308 (Weicker) discloses an arrangement of this type. A circular pressure vessel has a rotatable locking ring mounted on the vessel adjacent a circular aperture thereof, the ring having a series of inwardly facing lugs around its circumference. The door also has a series of outwardly facing lugs around its circumference, the ring lugs cooperating with the door lugs so that as the ring is rotated in a closing direction the door is locked by cam surfaces on the lugs, and as the ring is rotated in a reverse direction the ring and closure lugs move to an unlocked relationship in which the door can move axially away from the aperture. A generally similar arrangement is disclosed in U.S. Pat. No. 2,936,093 (Passalaqua) and in U.S. Pat. No. 3,804,288 (Piegza).